A Russian billionaire has paid more than £20m for an art collection owned by late cellist Mstislav Rostropovich, days before it was due to be auctioned.

Alisher Usmanov, a mining and metals magnate and Arsenal Football Club investor, said he stepped in to keep the 450 artworks together in Russia.

Sotheby's has cancelled its London auction, where the items were due to be sold individually later this week.

The buyer paid a "substantially higher" sum than the £20m estimate, it said.

"When I knew that this collection would be sold at auction, I felt the need to try to preserve the collection in its entirety," Mr Usmanov told Russian state-run television.

Rostropovich was one of the finest cellists of the 20th century

"The second goal, which is even more important, is to return [the collection] to the country that the art belongs to - Russia."

He intended to hand the collection over to the state, he added.

The artworks had been assembled by Rostropovich and his wife Galina Vishnevskaya.

Vishnevskaya's family said they were "delighted" the collection would be kept intact and described the sale as "especially meaningful" as the buyer would return all of the items to Russia.

'Invaluable'

The head of Russia's federal culture agency, Mikhail Shvydkoi, also welcomed the sale, saying that "for Russian culture and Russia as a whole, all things relating to the name of Mstislav Rostropovich are invaluable".

Rostropovich, who died in April at the age of 80, was considered one of the finest cellists of the 20th century.

He and his wife amassed one of the world's finest private collections of Russian art, including glassware, porcelain and works by leading painters such as Ilya Repin and Boris Grigoriev.

Mr Usmanov, one of Russia's richest men, is estimated to be worth $5.5bn (£2.8bn). He recently bought a 14.6% stake in Arsenal for £75m.